Warlocks - Warlock demons have a wide selection of names based on the demon type. This only affects new demons; existing demons will keep their names. - Warlocks can no longer kill players in duels.- Death Coil won't give health until it actually hits the target. - Death Coil will only give the amount of health that it actually drained from the target. - Create Soulstone: Reduced the Soul Shard cost from two shards to one shard. - Curse of Shadow: Increased duration from two minutes to five minutes. - Curse of the Elements: Increased duration from two minutes to five minutes. - Fear: Players now have an increasing chance to break free of the effect, such that it is unlikely the effect will last more than 15 seconds. - Devour Magic (Felhunter): Fixed a bug where the felhunter would be healed every time the spell was used, in addition to the healing gained from successful dispelling. - Tainted Blood (Felhunter): The reactive effect no longer causes threat. - Training costs adjusted. Total training cost was decreased. - Enslave Demon: Can no longer be cast on tapped targets.

Duels and PvP are different. PvP refers to killing the Alliance (if you're a Horde and vice versa). I'm guessing there was some sort of bug in the system that allowed you to kill players while duelling. I never encountered it, however.